1. Field of the Invention
The present invention relates to an apparatus for forming a cup-shaped cage as an outer member of a universal joint such as a ball joint.
2. Description of the Related Art
One kind of such apparatus is disclosed in Japanese Patent Application First Publication No. 59-24545. The apparatus includes an outer die retaining a cup-shaped workpiece for a cup-shaped cage and a plurality of inner die segments moveable relative to the outer die. The cup-shaped workpiece includes a shaft portion and a cup-shaped body portion connected with the shaft portion. The outer die retains the shaft portion of the cup-shaped workpiece and a bottom part of the cup-shaped body portion thereof which is disposed adjacent the shaft portion. A plurality of press-forming members are circumferentially arranged on the outer die. The press-forming members are adapted to be moved relative to a radially expanding part connected with the bottom part of the cup-shaped workpiece. The press-forming members each have surfaces of a predetermined shape and come into engagement with an outer circumferential surface of the radially expanding part. The inner die segments include pivotal portions each rotatable about a pin and formed with outer surfaces configured to a predetermined shape. A mandrel forces the inner die segments to move into an inside space of the cup-shaped cage and urges the pivotal portions to rotationally move into a press position in which the outer surfaces of the pivotal portions are brought into engagement with an inner surface of the cup-shaped workpiece.
In the above-described kind of apparatus, the outer die retains the bottom part of the cup-shaped body portion of the cup-shaped workpiece without a clearance therebetween. With this arrangement, in a case where the bottom part of the cup-shaped body portion of the workpiece has an uneven inner surface with a projection, the pivotal portions of the inner die segments are likely to be prevented from moving into the press position by abutting on the projection so that the inner surface of the cup-shaped workpiece cannot be formed into a configuration conformed to the predetermined shape of the outer surfaces of the pivotal portions. This tends to cause failure of forming the outer surface of the cup-shaped workpiece into a shape conformed to the predetermined shape of the surface of the press-forming members of the outer die.